<template>
  <canvas id="bg-canvas" ref="canvas"></canvas>
</template>

<script>
let timer = null;
export default {
  mounted() {
    //定义画布宽高和生成点的个数
    var WIDTH = this.$refs.canvas.offsetWidth,
      HEIGHT = this.$refs.canvas.offsetHeight,
      POINT = 35;

    var canvas = document.getElementById("bg-canvas");
    (canvas.width = WIDTH), (canvas.height = HEIGHT);
    var context = canvas.getContext("2d");
    (context.strokeStyle = "rgba(0,0,0,0.02)"), (context.strokeWidth = 1), (context.fillStyle = "rgba(0,0,0,0.05)");
    var circleArr = [];

    //线条：开始xy坐标，结束xy坐标，线条透明度
    function Line(x, y, _x, _y, o) {
      (this.beginX = x), (this.beginY = y), (this.closeX = _x), (this.closeY = _y), (this.o = o);
    }
    //点：圆心xy坐标，半径，每帧移动xy的距离
    function Circle(x, y, r, moveX, moveY) {
      (this.x = x), (this.y = y), (this.r = r), (this.moveX = moveX), (this.moveY = moveY);
    }
    //生成max和min之间的随机数
    function num(max, _min) {
      var min = arguments[1] || 0;
      return Math.floor(Math.random() * (max - min + 1) + min);
    }
    // 绘制原点
    function drawCricle(cxt, x, y, r, moveX, moveY) {
      var circle = new Circle(x, y, r, moveX, moveY);
      cxt.beginPath();
      cxt.arc(circle.x, circle.y, circle.r, 0, 2 * Math.PI);
      cxt.closePath();
      cxt.fill();
      return circle;
    }
    //绘制线条
    function drawLine(cxt, x, y, _x, _y, o) {
      var line = new Line(x, y, _x, _y, o);
      cxt.beginPath();
      cxt.strokeStyle = "rgba(0,0,0," + o + ")";
      cxt.moveTo(line.beginX, line.beginY);
      cxt.lineTo(line.closeX, line.closeY);
      cxt.closePath();
      cxt.stroke();
    }
    //初始化生成原点
    function init() {
      circleArr = [];
      for (var i = 0; i < POINT; i++) {
        circleArr.push(drawCricle(context, num(WIDTH), num(HEIGHT), num(15, 2), num(10, -10) / 40, num(10, -10) / 40));
      }
      draw();
    }

    //每帧绘制
    function draw() {
      context.clearRect(0, 0, canvas.width, canvas.height);
      for (let i = 0; i < POINT; i++) {
        drawCricle(context, circleArr[i].x, circleArr[i].y, circleArr[i].r);
      }
      for (let i = 0; i < POINT; i++) {
        for (let j = 0; j < POINT; j++) {
          if (i + j < POINT) {
            let A = Math.abs(circleArr[i + j].x - circleArr[i].x),
              B = Math.abs(circleArr[i + j].y - circleArr[i].y);
            let lineLength = Math.sqrt(A * A + B * B);
            let C = (1 / lineLength) * 7 - 0.009;
            let lineOpacity = C > 0.03 ? 0.03 : C;
            if (lineOpacity > 0) {
              drawLine(context, circleArr[i].x, circleArr[i].y, circleArr[i + j].x, circleArr[i + j].y, lineOpacity);
            }
          }
        }
      }
    }

    //调用执行
    init();
    timer = setInterval(function() {
      for (var i = 0; i < POINT; i++) {
        var cir = circleArr[i];
        cir.x += cir.moveX;
        cir.y += cir.moveY;
        if (cir.x > WIDTH) cir.x = 0;
        else if (cir.x < 0) cir.x = WIDTH;
        if (cir.y > HEIGHT) cir.y = 0;
        else if (cir.y < 0) cir.y = HEIGHT;
      }
      draw();
    }, 60);
  },
  beforeDestroy() {
    if (timer) {
      clearInterval(timer);
    }
  }
};
</script>

<style scoped>
#bg-canvas {
  width: 100%;
  height: 100%;
}
</style>
